TW201910940A - Method and device for illuminating digital full image by structured light - Google Patents

Abstract

A method of structured illumination digital holography includes: (a) providing a structured illumination generating unit and binarization random number encoding unit to generate a coded structured illumination pattern; (b) sampling at least two patterns with phase shift which synthesized as a single structured illumination pattern to be encoded; (c) forming a single digital hologram, and wavefront reconstructing the single digital hologram; (d) performing a compressive sensing approach to recover the object wave with at least two phase shift patterns; and (e) reconstructing the separation of overlap spectrum, to obtain an image covering bandpass spectrum with different high frequency and low frequency.

Description

   Method and device for structured light illumination digital hologram   

The invention relates to digital holographic microscopy technology, in particular to a method of combining structured light object light waves and reference light waves for interference and wavefront recording to reconstruct the microscopic and tomographic information of the object to be measured. With device.

The Department of Digital Holography Microscopy has been widely studied as one of the techniques for quantitative phase imaging in recent years. It can realize the object reconstruction method of numerical focusing, and has the quantitative phase analysis capability of sub-wavelength level. However, it is also affected by the optical diffraction limit, so that the wavelength of the light source and the limited aperture size will limit its spatial resolution and cannot break the resolution limit of half wavelength between two points. Therefore, synthetic holographic digital holography microscopy has been proposed to improve the spatial resolution of optical systems. Methods include: placing diffraction gratings to turn high-frequency information of objects, and mechanically moving image sensors to capture wide The diffraction information of the field of view, and the use of angle multiplexing to capture high-frequency information from various angles of the object to achieve spatial resolution improvement.

At present, the horizontal resolution that can be achieved in the technical field of synthetic aperture can reach 90 nanometers (nm), which is combined with the complex amplitude deconvolution method to complete the wavefront reconstruction of sub-micron objects. In the above method, the use of a mechanical galvanometer to rotate the angle of incidence of the light beam to scan the object is one of the main methods of synthetic aperture. However, such mechanical scanning will cause additional disturbances and the inability to accurately adjust the angle of incidence. This will limit the accuracy of the displacement spectrum of the synthetic aperture and affect the phase sensitivity.

Therefore, digital holography microscopy of structured light illumination is proposed to realize a synthetic aperture method without mechanical scanning, which can use a diffraction grating to divide the incident light into zero order (0 ^th ) and positive and negative first order (± 1 ^st ), And place a pinhole filter to remove the negative first-order (-1 ^st ) diffraction term, and then filter the zero-order (0 ^th ) diffraction term to become the low-frequency plane reference light wave output, and then The positive first-order (+1 ^st ) diffraction term interferes with the diffracted light waves of the object to form a hologram. In addition, there is a structured light method that uses a liquid crystal spatial light modulator to replace the diffraction grating. It uses a series of holographic patterns and uses a phase recovery algorithm to reconstruct the wavefront information of the object.

However, the above-mentioned structured light digital holographic microscope systems all require complex optical architectures to avoid crosstalk interference in different frequency bands, and are limited to detect projection stripes of known structured light to perform displacement spectrum correction, which cannot be targeted. The scattering spectrum of the object is expanded by the synthetic spectrum, which will make the measurement system sensitive to environmental disturbances and reduce the phase sensitivity, and the recording process is complicated and the spatial resolution cannot be enhanced.

In addition, due to the spectral overlap phenomenon of the bandpass spectrum of the object light wave, at least two phase shift patterns need to be taken to separate the spectral overlap, and the spectral overlap problem is solved and different high-frequency and low-frequency bandpasses are reconstructed Spectrum. However, such time multiplexing will make the phase sensitivity vulnerable to interference from the external environment and affect the signal-to-noise ratio of the reconstructed image.

In view of the shortcomings of the above-mentioned conventional technologies, it is really necessary to develop a novel structured lighting digital holography technology to solve and overcome these problems.

The digital holography method and device of structured light illumination provided by the present invention can realize super-resolution object wavefront reconstruction without using complex optical architecture to avoid frequency band crosstalk interference, and have real-time online operation potential.

The present invention uses structured light to illuminate the object to be measured so as to generate Moiré stripes to create a digital holographic recording method. It also uses the structured light of known spatial frequency and the convolution and correlation characteristics of the Moiré fringes scattered by the object under test to complete the image reconstruction and resolution improvement.

The invention provides a method for illuminating a digital hologram of structured light, including: (a) providing a structured light generating unit and a binary random number coding unit to generate coded structured light patterns; (b) by the structured light At least two binarized random coding patterns of the pattern, to sample at least two patterns with phase shift, and synthesize into a single structured light pattern with coding; (c) Illuminate the structured light pattern For an object, to form a single structural object light wave with coding and interfere with the reference light wave to produce a single digital hologram, and then perform wavefront reconstruction of the single digital hologram; (d) Binary chaos Digitally decode the pattern of the single digital hologram to extract the corresponding object light waves with phase shift patterns, and restore at least two object light waves with phase shift patterns by an image processing method; and (e ) A reconstruction method of performing overlapping spectral separation on the at least two object light waves with phase shift patterns to obtain images with different high-frequency and low-band pass spectrum coverage areas.

The structured light generating unit and the binary random number coding unit include a spatial light modulator, a digital micromirror device, and a diffraction grating. The single structured light pattern with coding includes imaging or non-imaging diffraction light waves.

In step (c), the form of the single digital hologram includes coaxial, off-axis, coaxial and common optical path. The wavefront reconstruction methods include temporal filtering method, spatial filtering method, and phase checking method. In this step (d), the image processing method includes a compression sensing method, a deconvolution method or an interpolation method. In step (e), the different high-frequency and low-band pass spectrums include two-dimensional and three-dimensional Fourier spectrum information.

The invention provides a device for illuminating a digital hologram with structured light, including: an emitting light source; an optical beam expander for emitting light emitted by the light source to form an expanded beam; at least one beam splitter for dividing the emitted light At least two light sources, or a combination of at least two light sources; a structured light generating unit for forming the structured light pattern with arbitrary spatial frequency and various directions; a binary random number coding unit for The emitted light is formed into a binary random number coding pattern with arbitrary spatial frequency and various directions; an illumination objective lens group is used to enlarge or reduce the structured light to facilitate irradiation to the object to be measured to form the object light; a receiving Objective lens group to enlarge or reduce the structured light to facilitate the formation of the object light as an imaging or non-imaging diffracted light wave; a reference light to interfere with the object light to form a structured light digital hologram; and a light The detector array is used to record the structured light digital hologram formed after the object light interferes with the reference light.

The form of the digital hologram includes coaxial, off-axis, coaxial, or common light programs.

The above structured light illuminating digital holographic device further includes a plurality of mirrors to change the light path of the emitting light source; and an optical relay objective lens group to modulate the high or low frequency of the light wave of the object to facilitate various optical Engineering procedures; the binary random number coding pattern can be in the form of amplitude or phase, while the structured light can be in the form of amplitude or phase.

A device for illuminating digital hologram with structured light, including: an emitting light source; an optical beam expander for forming an expanded beam of light emitted by the emitting light source; at least one beam splitter for dividing the emitted light into at least two Light sources, or a combination of at least two light sources; a plurality of mirrors to change the light path of the emitting light source; a structured light generating unit to form a structured light pattern with arbitrary spatial frequency and various directions for the emitted light Grain; Binary random number coding unit, used to make the emitted light form a binary random number coding pattern with arbitrary spatial frequency and various directions; an illumination objective lens group, used to enlarge or reduce the structured light, in order to facilitate Illuminate the object to be measured to form object light; a receiving objective lens group to enlarge or reduce the structured light to facilitate the formation of the object light as an imaging or non-imaging diffracted light wave; and a light detector array to Record the structured light digital hologram after the object light interferes with the reference light.

In one point of view, the device for illuminating digital holograms further includes a grating to generate light wave information of the object at different diffraction orders; and an optical relay system to modulate the light wave of the object to facilitate the Optical multiplexing with different diffraction orders.

In another aspect, the above structured light illuminating digital hologram device further includes a second optical relay system, a filter cover and a grating, wherein the grating is disposed in the receiving objective lens group and the second optics Between the two systems, and the filter mask is disposed between the two sets of lenses in the second optical relay system.

In yet another aspect, the above structured light illuminating digital holographic device further includes a second optical relay system and a grating, wherein the grating is disposed on a side of the second optical relay system, and the filter The mask is embedded in the grating.

These advantages and other advantages will enable the reader to clearly understand the present invention from the description of the following preferred embodiments and the scope of patent application.

100‧‧‧Emitting light source

101‧‧‧spatial filter (SF)

102, 103, 104, 118, 140 ‧‧‧ beam splitter

105、121‧‧‧Spatial light modulator (SLM)

TL1‧‧‧Illumination objective lens group

TL2‧‧‧Receive objective lens group

TL3‧‧‧Optical Relay System

106‧‧‧Light detector array

107, 108, 116, 125‧‧‧‧Linear polarizer

109, 110, 124 ‧‧‧mirror

111‧‧‧ Optical Beam Expander

112, 115, 117, 123, 126, 135, 136, 160 ‧‧‧ lens

113, 114‧‧‧microscope objective lens (microscope objective lens)

119, 122‧‧‧ optical mask

120‧‧‧incident light

130, 306‧‧‧ Reference light

131‧‧‧ grating

132‧‧‧filter mask

133‧‧‧First filter area

134‧‧‧Second filter area

150、304‧‧‧Object to be measured

200, 201, 202, 203, 204 ‧‧‧ steps

300‧‧‧Irradiation light source

301‧‧‧Optical system

302‧‧‧At least two patterns with known spatial frequency structure

303‧‧‧ At least two known binary random number coding patterns

305‧‧‧ Fresnel diffraction

307‧‧‧Single structured light digital hologram

308‧‧‧Wavefront reconstruction algorithm

309‧‧‧ Take out at least two known binary random number coding patterns

310‧‧‧Compression sensing

311‧‧‧Reply at least two objects with phase shift pattern light waves

312‧‧‧ Overlapped spectrum separation and reconstruction method

313‧‧‧ Fourier transform

314‧‧‧ spectrum overlap

315‧‧‧Inverse Fourier Transform

316‧‧‧ Wavefront reconstruction image with high spatial resolution

317‧‧‧ amplitude image

318‧‧‧phase image

The detailed description of the present invention and the schematic diagrams of the embodiments as described below should make the present invention more fully understood; however, it should be understood that this is only a reference for understanding the application of the present invention and does not limit the present invention to a specific implementation Cases.

The first figure shows a schematic diagram of a structured light digital hologram device according to an embodiment of the present invention; the second figure shows a schematic view of a structured light digital hologram device according to another embodiment of the present invention; FIG. 3 shows a schematic diagram of a structured light digital holography device according to yet another embodiment of the invention; FIG. 3 shows a schematic view of a structured light digital hologram device according to still another embodiment of the invention; The third diagram B shows a schematic diagram of a structured light digital hologram device according to yet another embodiment of the invention; the fourth diagram shows a flow chart of a structured light digital hologram method according to the invention; the fifth diagram shows A detailed flowchart of a digital hologram of structured light illumination according to an embodiment of the present invention; Figure 6 shows a schematic diagram of two binary random number coding patterns according to the present invention; Figure 7 shows two images according to the present invention A schematic diagram with a phase shift pattern; the eighth figure shows a schematic diagram of the structured light pattern after the two phase shift patterns according to the present invention are sampled by the binarized random code pattern; the ninth figure A shows The schematic diagram of the image information of the object to be measured according to the present invention; the ninth figure B shows a schematic diagram of a single object light wave with a coding structure according to the present invention; the tenth figures A to B show the phase shift codes are 0 ° And a schematic diagram of the light wave of the object with the phase shift pattern corresponding to the 120 ° binary random decoding pattern; Figures 11 to 11 show that the phase shift codes are 0 ° and 120 ° respectively A schematic diagram of two light waves of an object with a phase shift pattern restored by a compression sensing algorithm; Figures 12 to 12 show that the diffraction order corresponding to the spectrum is a positive first order (+1 ^st ), negative first-order (-1 ^st ) schematic diagram of the band-pass spectrum; Figures 13 to 13 show that the corresponding diffraction order of the spectrum is positive first order (+1 ^st ), negative one -Level (-1 ^st ) reconstructed amplitude image; Figure 14 shows the range of the 2D synthetic spectrum covered by the two-dimensional Fourier transform synthesis method to synthesize 2D high spatial resolution wavefront imaging; Figure 14 shows B The two-dimensional Fourier transform synthesis method is used to synthesize the two-dimensional high spatial resolution wavefront component Synthesized amplitude reconstructed image; Figure 14 shows the two-dimensional Fourier transform synthesis method to synthesize two-dimensional high-spatial-resolution wavefront imaging synthetic phase reconstructed image; Figure 15 shows the simulated three-dimensional object through three-dimensional Fourier spectrum synthesis Method; Figure 16 shows the coverage of the three-dimensional synthesis spectrum in xy space; Figure 16 shows the coverage of the three-dimensional synthesis spectrum in yz space; Figure 16 shows the refraction of the three-dimensional synthesis spectrum in xy space Tomographic reconstruction of the rate; Figure 16 D shows the tomographic reconstruction of the refractive index of the three-dimensional synthetic spectrum in the yz space.

Herein, the present invention will be described in detail with respect to specific embodiments of the invention and their viewpoints. Such descriptions are used to explain the structure or steps of the present invention, which are provided for illustrative purposes rather than to limit the scope of the patent application of the present invention. Therefore, in addition to the specific embodiments and preferred embodiments in the specification, the present invention can be widely implemented in other different embodiments.

The invention uses structured light to irradiate the object to be tested to generate Moiré fringes to create a digital holographic recording method, and uses structured light of known spatial frequency and the convolution and correlation between the Moiré fringes scattered by the object to be tested ) Features to complete image reconstruction and resolution enhancement.

The device provided by the present invention includes: at least one set of structured light for illuminating the object to be measured to generate Moiré stripes; at least one set of reference light; at least one digital holographic wavefront access unit.

The method proposed in the present invention utilizes the reconstructed image of the lower spatial frequency Moiré fringe digital hologram obtained from each frequency band and the known higher spatial frequency structured light to perform de-convolution and mutual correlation. The operation is to complete the displacement spectrum correction and spectrum overlapping, to realize the super-resolution reconstruction image of spectrum expansion. In the embodiment, the phase shift and rotation angle of structured light with known spatial frequency are used for multiple exposures, and combined with singular value decomposition (SVD) and pseudo-inverse matrix (pseudo-inverse matrix) operations to separate structured light illumination The cross-talk interference in each frequency band. Then, the correlation characteristics are used to perform cross-correlation operation between the object to be measured and the reconstructed image of the Moiré fringe digital hologram at a lower spatial frequency to achieve the extension of the isotropic synthesized spectrum.

The embodiment of the present invention points out a digital hologram formed by capturing the light of the Moiré fringe object scattered by the object to be measured at a lower spatial frequency and interfering with the plane / spherical reference light, and using the phase shift and angle to rotate the known spatial frequency structure Multiple exposures of light to achieve separation of crosstalk in the frequency band.

In order to meet the above technical problems and needs, the present invention provides a method and device for structured light illumination digital holography. This holographic image can be reconstructed by a computer to obtain a complex image, which includes amplitude and phase information, and is not limited to the pixel and pixel size of the photodetector array.

The present invention proposes to use a spatial light modulator to generate a single structured light pattern with coding, and to use a compressive sensing algorithm to recover at least two object light waves with phase shift patterns. Separate reconstruction methods by overlapping the spectrum to obtain images with different high-frequency and low-band pass spectrum coverage. This will make the proposed method and device for illuminating digital holograms of structured light free from the time multiplexing limitation of shooting multiple phase shift patterns, and can further achieve the high spatial resolution wavefront reconstruction method for single exposure.

The first figure shows a structured light digital holographic device according to an embodiment of the invention. In this embodiment, the structured light pattern will act on the object light wave to generate different high-frequency and low-band pass spectrums. The bandpass spectrum of the light waves of these objects can be used to synthesize the spectrum to expand the coverage of the spectrum and to improve the spatial resolution of the reconstructed image.

The present invention proposes to use at least two binary random number codes to sample the at least two phase shift patterns. In one embodiment, the structured light pattern uses a second-order phase grating with a phase difference of π as the input pattern of the structured light generating unit, and the expression of the pattern is as follows:

Among them, the grating period is Λ = 2 w , and the impulse response function (point spread function) of the illumination objective lens group is h _TL ( y ). The Fourier transform of the structured light pattern can be expressed as a combination of different diffraction orders as follows:

Each diffraction order of the structured light pattern is m , and the maximum diffraction efficiency output can be achieved at the diffraction order of ± 1 ^st . The coherent transfer function of the illumination objective lens group is ( v ). In this structured light pattern, the spatial frequency of the grating period is set to the maximum receivable angle of the coherent transfer function, so as to cut off the noise interference generated by each high-order diffraction term. The binary random number coding pattern is to modulate the structured object light wave through the optical relay objective lens group, and perform spatial multiplexing of ± 1 ^st diffraction order to form the structured light pattern object light wave with coding. The random number encoding unit will generate a binary phase encoding pattern, and act on the ^-1st diffraction order object light wave to form the encoded object light wave, which can be expressed as follows:

Among them, the binary phase encoding pattern is exp [ i Φ _n ( x , y )], the angle diffracted by the grating period is sin θ _m , and the object o _d ( x , y ) will be placed in the defocus plane The above is used to perform the compression sensing algorithm, and its expression is as follows:

The diffraction distance is z _R and the original object is o ( ξ , η ). Interference between the above-mentioned coded object light wave and the +1 ^st object light wave to form a coded structured light object light wave, then interferes with the off-axis reference light wave to form a digital hologram, and the coded structured light is obtained after wavefront reconstruction Object light waves are as follows:

Among them, the incident angle of the off-axis reference light is sin θ _{x '} and sin θ _y' . After the numerical reference light is corrected, the coherent transfer function of the illumination objective lens group and the receiving objective lens group and the reconstruction information of the encoded object light wave can be obtained as follows:

Among them, the coherent transfer function of the illumination objective lens group is ( f _SI , 0), the coherent transfer function of the receiving objective lens group is ( u , v ), and the spectrum coverage of the light waves of the encoded object are respectively ( u - f _SI , v ) and ( u , v - f _SI ). However, the encoding structure with the binary phase pattern can be combined with the compression sensing algorithm and the light wave to restore two objects with phase shift patterns, and can be through singular value decomposition (SVD) and pseudo-inverse A matrix (pseudo-inverse matrix) operation to obtain ± 1 ^st diffraction order object light waves is as follows:

among them, ( u , v ) and ( u , v ) are the object light waves of two phase shift patterns returned by the compression sensing algorithm, and exp ( i Φ ₁ ) and exp ( i Φ ₁ ) are generated by the binary phase pattern encoding Known phase shift, therefore, the bandpass spectrum will use spectral overlap separation and reconstruction method to obtain different high-frequency and low-band pass spectrum, and its synthetic superposition in the spectrum space will be used to enhance the spectrum coverage and express for:

The synthesized spectrum with extended spectrum coverage obtained through the above steps can be used to obtain high spatial resolution microscopic and tomographic object reconstruction images.

Refer to the first figure, which is a structured light illuminating digital hologram device according to an embodiment of the present invention. The invention is used to process a single digital holographic reconstruction image related to the object to be measured, and the digital holograms are generated by an optical system in the first image. The optical system includes an emission light source 100, a spatial filter (SF) 101, three beam splitters 102, 104 and 118, and two liquid crystal spatial light modulators (SLM) 105 121, an illuminating objective lens group TL1, a receiving objective lens group TL2, a photodetector array 106 (for example: Charge-coupled Device (CCD), Complementary Metal-Oxide-Semiconductor ; CMOS) and other image sensors, photodetectors (Photodetector)), four linear polarizers (polarizers) 107, 108, 116 and 125, three mirrors (mirror) 109, 110 and 124, and one Optical beam expander 111. For example, the illumination objective lens group TL1 includes a lens 112 having a focal length of 200 millimeters (mm) and a microscope objective lens 113 and 114 having a numerical aperture (NA) of 0.25. The front and back focal lengths of the lens 112 may be equal, or may be substantially equal but slightly different. The front and back focal lengths of the micro objective lens 113 may be equal, or may be substantially equal but slightly different. The receiving objective lens group TL2 includes a micro objective lens 114 having a numerical aperture (NA) of 0.25 and a lens 115 having a focal length of 200 millimeters (mm). The front and back focal lengths of the microscope objective 114 may be equal, or may be substantially equal but slightly different. The front and back focal lengths of the lens 115 may be equal, or may be substantially equal but slightly different. The reference light 130 may be a plane wave distribution or a spherical wave distribution. In an embodiment, the illumination objective lens group TL1 is an optical imaging reduction system (Telescopic Imaging System), and the receiving objective lens group TL2 is an optical relay system.

The emission light source 100 includes a vertical resonant cavity surface-emitting laser (Vertical-Cavity Surface-Emitting Laser; VCSEL), a semiconductor laser (Semiconductor laser), a solid-state laser (Solid-state laser), a gas laser (Gas laser), Liquid laser (Dye laser), fiber laser (Fiber laser) or light emitting diode (LED). The light source form of the emission light source 100 includes a linear light source, a planar light source or a spherical light source. The light source characteristics of the emission light source 100 include coherent light sources, low coherent light sources, or non-coherent light sources. For example, the emission light source 100 is a diode-pumped solid-state (DPSS) laser source. In one example, this diode-pumped solid-state laser source generates a laser light with a wavelength of 532 nanometers (nm). The optical path of the optical system of the device includes: the laser light first passes through the spatial filter 101, and then passes through an optical beam expander (such as a lens) 111 to generate a completely expanded beam (such as a collimated plane wave), the laser light After being reflected by the mirror 109, it enters the beam splitter 102 and outputs two beams respectively. One of the light beams 120 first passes through the linear polarizer 107 to change the polarization state of the incident light, and then passes through the dichroic mirror 102 to enter the liquid crystal spatial light modulator 105 to generate a structured light pattern. The incident light 120 is additionally reflected by the beam splitter 102 to the linear polarizer 108 to realize the output mode of the phase modulation mode. Next, the structured light pattern is output from the illumination objective lens group TL1 (112 & 113) to be illuminated on an object to be measured 150, and a coded structured object light wave is formed. Wherein, the structured light pattern is synthesized into a single structured light pattern with coding through at least two patterns with phase shift. That is, the single piece of structured light pattern with phase shift is illuminated on the object to be measured 150 to form an object wave of the structured object, and the object will be placed in the Fresnel region. Then, the object light wave passes through the receiving objective lens group TL2 (114 & 115) for micro imaging. Next, the optical Fourier transform of the light wave of the structured object through the lens 117 forms a diffracted light wave of positive first order (+ 1st) and negative first order (-1st). The reflected beam will pass through the spatial optical mask ( y- direction optical block) 119, and the optical mask 119 will eliminate the negative first-order (-1st) diffracted light waves (used to block the + 1st-order diffraction term and let the -1st-order diffraction Ray item passes), the penetrating beam will pass through the spatial optical mask (optical block in the x direction) 122, and the optical mask 122 will eliminate the positive first order (+ 1st) diffracted light wave (used to block the +1 order diffracted term, Let the -1 order diffraction item pass); the black dots represent the optical block, used to block the light through; the white circle represents the remaining light through. The positive first-order (+ 1st) diffracted light wave will pass through the lens 160 and be imaged into the binary random code pattern generating unit 121 to sample the structure object light wave. The polarizing plate 116 and the analyzer 125 are used to modulate the optical characteristics of the binarized random code generating unit 121. Similarly, the transmitted light beam will pass through the optical mask to eliminate the positive first-order (+ 1st) diffracted light waves, while the negative first-order (-1st) diffracted light waves pass through the lens 123 and are imaged onto the 124 mirror. The positive first-order (+ 1st) diffracted light wave and the negative first-order (-1st) diffracted light wave modulated by the above-described binarized random number coding generating unit will be reflected along the original path and formed by the beam splitter 118 The encoded structural object light wave is imaged by the lens 126 onto the image sensor 106. Another plane reference light wave 130 is reflected by the mirror 110 and then enters the dichroic mirror 104, and then enters the image sensor 106 at the same time. The reference light wave and the normally incident object light wave maintain an off-axis angle for off-axis digital holographic recording, and ensure that the object light wave formed when the structured light pattern is illuminated to the object 150 can meet the reference The light wave is maintained in an off-axis recording architecture that eliminates DC terms and conjugate terms.

The above structured light may be in the form of light waves of amplitude or phase, and the binary random number coding may be in the form of light waves of amplitude or phase. The digital hologram can be coaxial, off-axis, coaxial or co-optical, and the reference light can be flat, spherical or any light wave form. The structured lighting digital holography device further includes an object loading platform (not shown) for placing the object to be measured 150, and has a displacement mechanism for adjusting the xyz axis.

Some embodiments are suitable for processing at least one off-axis recording architecture related to a resolution criterion that can eliminate DC terms and conjugate terms. As shown in the first figure, the three reflecting mirrors 109, 110 and 124 are only used to change the optical path of the laser light. The lens 111 can be other elements (planar and spherical waves) that can generate a beam-expanded wavefront. The above-mentioned lenses 112 and 115 may be other elements that can generate a flat, spherical and arbitrary curved wavefront.

It is worth mentioning that: in the embodiment of the first picture above, an improved Mach-Zehnder interferometer is adopted by the optical system to realize a single structured light pattern with coding Digital holographic recording method that illuminates objects and interferes with off-axis reference light waves. The convolution between the structured light pattern and the stripes of the object to be measured will be used to break through the limit of the optical diffraction limit. In other embodiments, the digital holograms of the fringe images can also be transmitted, such as diffractive optical elements, combining spatial multiplexing and angular multiplexing, and other structured light illumination technologies such as spatial light modulators, digital micromirror devices, etc. Generate on-axis, off-axis, in-line, or common-path digital transmission through the reflection / reflection type holographic recording.

Refer to the second figure, which is a structured light illuminating digital hologram device according to another embodiment of the present invention. The invention is used to process a single digital holographic reconstruction image related to the object to be measured, and the digital holograms are generated by an optical system in the second figure. The optical system includes an emitting light source 100, a spatial filter 101, three beam splitters 102, 103 and 104, a liquid crystal spatial light modulator 105, an illumination objective lens group TL1, a receiving objective lens group TL2, and a light detector The array 106, two linear polarizers 107 and 108, two reflecting mirrors 109 and 110, and an optical beam expander 111. The optical path of the optical system and the function of each element can refer to the description in the first figure. In another embodiment, as shown in the third figure, the optical system omits the dichroic mirrors 102 and 104, and the remaining components are the same as those in the second figure.

In another embodiment, as shown in FIG. 3A, the optical system omits the beam splitters 102 and 104, and a set of optical relay systems (optical image reduction systems) TL3 and a grating are added to the optical system. Grating) 131 and a filter mask 132. The grating 131 is disposed between TL2 (receiving objective lens group) and TL3, and the filter mask 132 is disposed between the two lenses 135 and 136 of the optical image reduction system TL3. The filter mask 132 includes a first filter area 133 and a second filter area 134, wherein the first filter area 133 can pass object light, and the second filter area 134 can pass reference light.

In another embodiment, as shown in FIG. 3B, the optical system omits the beam splitters 102 and 104, and a new optical relay system (optical image reduction system) TL3 and a grating are added to the optical system. For example, Blazed grating 131. TL3 includes a lens 135, a lens 136, and a beam splitter 140. The lens 135 is disposed on the left side of the dichroic mirror 140, and the lens 136 is disposed on the upper side of the dichroic mirror 140. The dichroic mirror 140 is disposed between the lens 135 and the grating 131. The grating is disposed on one side of the optical relay system TL3, and the filter mask is embedded in the grating 131. The filter mask includes a first filter area 133 and a second filter area 134, wherein the first filter area 133 is for the peripheral distribution after the light wave is focused, and the peripheral grating is used to modulate the object light, and the second filter area 134 is for For the central part after the light wave is focused, the grating in the center is modulated to form the reference light.

The fourth figure shows a flow chart of a method for illuminating a digital hologram with structured light according to the present invention. The method of structured light illumination digital holography of the present invention includes steps 200-204. First, proceed to step 200 to generate structured light patterns and binary random number coding patterns. In this step 200, a structured light generating unit and a random number coding unit are provided to generate a structured light pattern for illuminating an object to be measured and form a coded structured object light wave (binarized random number coding pattern) . The random number coding unit is, for example, a binary random number coding pattern. Among them, the structured light generating unit and the binary random number coding unit include a spatial light modulator, a digital micromirror device, a diffraction grating and other photoelectric modulation elements to form a binary random number coding pattern from the light emitted by the emitting light source, Structured light pattern at any spatial frequency and direction. In this embodiment, a liquid crystal spatial light modulator in phase mode is used to form a pattern with a phase shift and a binarized random coding pattern from the light emitted by the emitting light source; the spatial frequency of the patterns can be adjusted arbitrarily And the direction is illuminated to the object to form a coded structure object light wave.

Next, in step 201, at least two pieces of phase-shifted patterns are sampled by the at least two binarized random coding patterns, and synthesized into a single structured light pattern with coding for illumination at object. In this embodiment, a binary random number coding unit is used to generate two binary random number coding patterns, and the sampling points of the binary random number coding pattern do not overlap each other, as shown in the fourth figure. The sixth to eighth figures show the encoding method of structured light patterns, wherein the sixth figure includes two binary random number coding patterns. Then, the structured light generating unit is used to output two phase shift patterns. The phase shift pattern is shown in the seventh figure, where from left to right are phase shift patterns of 0 ° and 120 ° phase shift. The seventh figure shows two patterns with phase shift. And the binary random number coding pattern is sampled as the coded structured light pattern of the eighth image, the coded structured light pattern can be synthesized into a single structured light pattern with two phase shift codes, and the coded The structured light pattern can be imaging or non-imaging diffracted light waves. The eighth figure shows the structured light pattern after two phase shift patterns are sampled by the binarized random code pattern.

Then, in step 202, illuminate the single structured light pattern with two phase shift codes on an object to be measured to form a coded structured object light wave, and then interfere with the reference light wave to generate a single structured light Digital hologram and then wavefront reconstruction. The form of a single digital hologram includes coaxial, off-axis, coaxial and co-optical path. Wavefront reconstruction methods include temporal filtering, spatial filtering, and phase retrieval. In this embodiment, the phase-shift-encoded structured light pattern is reduced and imaged on the object to be measured as shown in the ninth figure A through the illumination objective lens group TL1, and the coded structured object light wave is enlarged and imaged in the intermediate image by the receiving objective lens group TL2 Plane; then propagate to the Fresnel diffraction area to form the encoded structural object light wave as shown in Figure 9B, and interfere with the off-axis reference light wave for spatial filtering (spatial filtering) wavefront reconstruction. The ninth picture A to the ninth picture B show a single light wave encoding method with an encoding structure object, wherein the ninth picture A contains the image information of the object to be measured, and the ninth picture B contains a single picture with the encoding structure Object light waves.

The light wave diffraction is, for example, Fresnel diffraction or Fraunhofer diffraction. In this embodiment, the diffraction information is imaged to the intermediate image plane of the object, and diffracted a distance to the Fresnel region to generate low-frequency diffraction fringe information, so as to solve the problem of the actual pixel size limitation of the photodetector array.

Next, in step 203, the binarized random number decoded wavefront reconstructed pattern of the structured object light wave (single digital hologram) to extract the corresponding object light wave with the phase shift pattern and use a Image processing method to recover at least two object light waves with phase shift patterns. In one embodiment, the image processing method includes: compressive sensing, de-convolution, or interpolation. The wavefront-reconstructed coded object light wave will use the binary random decoding pattern to extract the corresponding object light wave with the original phase shift pattern, as shown in Figures 10 to 10B. The tenth picture A to tenth picture B are the light waves of the object with the phase shift pattern extracted by the binary random decoding pattern. The phase shift codes are 0 ° and 120 ° with the phase shift. Patterned object light waves. The object light wave of the phase shift pattern will be compressed and calculated to return to the two object light waves with phase shift pattern as shown in Figure 11 to Figure 11 B. The phase shift codes are 0 ° And the 120 ° phase shift pattern of the object light wave reconstruction image.

Finally, in step 204, a reconstruction method of performing overlapping spectrum separation on the at least two object light waves with phase shift patterns to obtain images with different high-frequency and low-band pass spectrum coverage areas. In this embodiment, as shown in the twelfth image A to the thirteenth image B, it displays images with different high-frequency and low-band pass spectrum coverage areas obtained through the overlapping spectrum separation and reconstruction method, of which the twelfth Figures A to Twelfth Figure B show the corresponding band-pass spectra of the positive first-order (+1 ^st ) and negative first-order (-1 ^st ) diffraction orders corresponding to the spectrum, and Figures 13 to 13 Figure B shows the reconstructed amplitude images with the corresponding diffraction order of the spectrum as positive first order (+1 ^st ) and negative first order (-1 ^st ), respectively. These band-pass spectra can be synthesized by two-dimensional Fourier transform synthesis to synthesize two-dimensional high-resolution wavefront imaging, as shown in Figure 14 to Figure 14B. Among them, the fourteenth picture A is the coverage area of the two-dimensional synthesized spectrum, the fourteenth picture B is the synthesized amplitude reconstructed image, and the fourteenth picture C is the synthesized phase reconstructed image. In another embodiment, three-dimensional Fourier transform is used to achieve tomography. As shown in Figure 15, it is a simulation of a three-dimensional object undergoing three-dimensional Fourier spectrum synthesis to obtain a tomographic reconstruction image corresponding to the three-dimensional synthesized spectrum of Figures 16 to 16 D. Figure 16 shows the coverage of the three-dimensional synthetic spectrum in xy space, and Figure 16 shows the coverage of the three-dimensional synthetic spectrum in yz space. Figure 16 shows the tomographic reconstruction of the refractive index of the three-dimensional synthetic spectrum in the xy space, and Figure 16 shows the tomographic reconstruction of the refractive index of the three-dimensional synthetic spectrum in the yz space.

As described above, the sixth to sixteenth figures D are mainly digital holograms generated by a computer simulation of the structured light illumination digital hologram device as shown in the first to third figures. The structured light is used to illuminate the digital hologram method to obtain a synthesized spectrum with different high-frequency and low-band pass spectrum coverage and its high spatial resolution reconstructed image. In the computer simulation of the present invention, the spectrum coverage of structured light digital holography and the performance of structured light projection fringes in spatial resolution are provided. In another preferred embodiment, the center wavelength of 532 nm for analog light source (nm), the pixel size of micrometers △ x = 0.26 ([mu] m), the number of samples is 1538 × 1538. The test samples used contain several bright and dark stripes with different spatial frequencies, mainly including pairs of micrometers from 5.4, 3.6 to 1.8 micrometers (μm) to compare the effect of the combined spectrum after irradiation with structured light High spatial resolution amplitude and phase images. Therefore, the numerical aperture NA of the receiving objective lens group is set to 0.12 in the simulation, and the ideal resolution that can be achieved when the object to be measured is incident with the zeroth order (0 ^th ) diffraction term of structured light is 3.4 micrometers (μm), such as Figure 13 is shown in Figure A. Then, the positive and negative first-order (± 1 ^st ) diffraction terms of the structured light enter the object to be measured, and its spatial resolution can be increased to 1.7 micrometers (μm), as shown in FIG. 14B.

The fifth figure shows a detailed flowchart of a method for illuminating a digital hologram with structured light according to an embodiment of the invention. The illumination light source 300 generates an incident light to be incident on an optical system 301, and outputs two light beams (I ₁ , I ₂ ) respectively through a beam splitter. One beam (I ₁ ) first generates at least two patterns 302 with known spatial frequency structures, and the other beam (I ₂ ) serves as a reference wave 306. Next, the binary random number coding unit is used to generate at least two known binary random number coding patterns 303. Then, a single structured light pattern with coding is illuminated on the object to be measured 304 to form a coded structured object light wave. After that, the structured object light wave is subjected to Fresnel diffraction 305 to propagate to the Fresnel zone. The encoded structured object light wave of Fresnel diffraction 305 and the reference light wave 306 will reach the image sensor of the optical system 301 at the same time for digital holographic recording, and a single structured light digital hologram 307 is generated. Next, a wavefront reconstruction algorithm 308 is executed for a single structured light digital hologram, which includes diffraction orders of various orders. Then, at least two known binary random number coding patterns 309 are taken out for subsequent compression sensing 310. After compressing the sensing method, at least two object light waves 311 with phase shift patterns are restored. Afterwards, an overlapping spectrum separation and reconstruction method 312 is performed on the at least two object light waves with phase shift patterns. Next, the two-dimensional or three-dimensional Fourier transform 313 method is performed to facilitate super-resolution and tomography. Then, step 314 of spectrum overlapping is performed to synthesize the spatial coverage of the spectrum. Afterwards, an inverse Fourier transform 315 method is performed to form a wavefront reconstructed image 316 with high spatial resolution. The wavefront reconstructed image includes an amplitude image 317 and a phase image 318.

In summary, by using the method and device for illuminating digital hologram of structured light of the present invention, the convolution characteristic between the object light wave and the structured light pattern is used to complete the extended spectrum coverage, and the two-dimensional and three-dimensional Fourier spectrum The synthesis can realize the wavefront reconstruction of the super-resolution of the microscopic and fault space of the sample to be tested, so it can indeed achieve the purpose of the invention.

The method and device for digital holography of structured light illumination of the present invention can be applied to at least the following fields:

(1) Optical components: detection of defects on transparent glass substrates, detection of the height of microlens arrays, detection of glue flatness of integrated circuits, detection of defects of photoelectric components, oil stains, scratches, cracks, and detection of holes on silicon substrates.

(2) Integrated circuits and semiconductor components: component line width, line height, ball diameter, three-dimensional surface morphology, step height standard film, process stacking, break height, slope, volume, surface area, vibration mode.

(3) Micro-optical components: surface flaw detection, surface roughness, surface profile, film thickness and flatness, radius of curvature, wavefront measurement, aberration analysis, refractive index distribution can be used to detect the refractive index distribution inside the fiber.

(4) Biomedical cell imaging: cell biology, nerve cell observation, cell volume, cell morphology, biosensors, biochips, living biological cell detection and analysis, drug development and screening.

(5) Mobile phones and panels: 3D surface topography, stress and deformation, mobile phone lenses, defect detection, oil stains, fingerprints, cracks, dispensing, solder paste, coating, flatness, roughness, polishing.

In addition to what is described here, different improvements that can be achieved by the embodiments and implementations described in the present invention should be included in the scope of the present invention. Therefore, the drawings and examples disclosed herein are used to illustrate rather than limit the present invention, and the scope of protection of the present invention should only be based on the scope of the subsequent patent applications.

Claims (10)

    A method for illuminating a digital hologram of structured light, comprising: (a) providing a structured light generating unit and a binary random number coding unit to generate structured light patterns; (b) by at least two of the structured light patterns Zhang's binarized random number coding pattern, to sample at least two patterns with phase shift and synthesize into a single structured light pattern with code; (c) The single structured light pattern with code Illuminate an object to form a coded structure object light wave and interfere with the reference light wave to generate a single digital hologram, and then perform wavefront reconstruction of the single digital hologram; (d) Binary random decoding to the single A digital hologram pattern to extract the corresponding object light waves with phase shift patterns, and to recover at least two object light waves with phase shift patterns by an image processing method; and (e) the at least Two reconstruction methods of object light waves with phase shift patterns for overlapping spectrum separation to obtain images with different high-frequency and low-band pass spectrum coverage areas.         The method for illuminating a digital hologram of structured light as described in claim 1, wherein in the step (d), the image processing method includes a compression sensing method, a deconvolution product method or an interpolation method.         The method of structured light illumination digital holography as described in claim 1, wherein in step (e), the different high-frequency and low-band pass spectrums include two-dimensional and three-dimensional Fourier spectrum information.         A device for illuminating digital hologram with structured light, including: an emitting light source; an optical beam expander for forming an expanded beam of light emitted by the emitting light source; at least one beam splitter for dividing the emitted light into at least two Light sources, or a combination of at least two light sources; a structured light generating unit for forming the emitted light into a structured light pattern with any spatial frequency and various directions; a binary random number coding unit for making the emitted light The light forms a binary random number coding pattern with arbitrary spatial frequency and various directions; an illumination objective lens group is used to enlarge or reduce the structured light to facilitate irradiation to the object to be measured to form object light; a receiving objective lens group, Used to enlarge or reduce the structured light to facilitate the formation of the object light as an imaging or non-imaging diffracted light wave; a reference light to interfere with the object light to form a structured light digital hologram; and a light detector The array is used to record the structured light digital hologram formed by the interference between the object light and the reference light.         The device for illuminating a digital hologram of structured light as described in claim 4, wherein the form of the digital hologram includes coaxial type, off-axis type, coaxial type or common light program.         The device for illuminating digital holograms as described in claim 4 further includes a plurality of face mirrors to change the light path of the emitting light source; and an optical relay objective lens group to modulate the high frequency of the object light wave Or low frequency to facilitate various optical multiplexing procedures; the binary random number coding pattern may be in the form of amplitude or phase, and the structured light may be in the form of amplitude or phase.         A device for illuminating digital hologram with structured light, including: an emitting light source; an optical beam expander for forming an expanded beam of light emitted by the emitting light source; at least one beam splitter for dividing the emitted light into at least two Light sources, or a combination of at least two light sources; a plurality of mirrors to change the light path of the emitting light source; a structured light generating unit to form a structured light pattern with arbitrary spatial frequency and various directions for the emitted light Grain; Binary random number coding unit, used to make the emitted light form a binary random number coding pattern with arbitrary spatial frequency and various directions; an illumination objective lens group, used to enlarge or reduce the structured light, in order to facilitate Illuminate the object to be measured to form object light; a receiving objective lens group to enlarge or reduce the structured light to facilitate the formation of the object light as an imaging or non-imaging diffracted light wave; and a light detector array to Record the structured light digital hologram after the object light interferes with the reference light.         The device for illuminating digital holograms of structured light as described in claim 7 further includes a grating to generate light wave information of the object at different diffraction orders; and an optical relay system to modulate the light wave of the object to facilitate The optical multiplexing of the different diffraction orders.         The structured light illuminating digital holographic device as described in claim 8 further includes a second optical relay system, a filter cover and a grating, wherein the grating is disposed in the receiving objective lens group and the second optics Between the two systems, and the filter mask is disposed between the two sets of lenses in the second optical relay system.         The structured light illuminating digital holographic device as described in claim 8 further includes a second optical relay system and a grating, wherein the grating is disposed on one side of the second optical relay system, and the filter The mask is embedded in the grating.